EVALUATION OF GENERAL ANESTHETICS IN RELATION TO TRIGEMINO-AUTONOMIC REFLEX

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We investigated effects of general anesthetics on trigeminal depressor responses ( TDR), which were evoked with electrical stimulation to trigeminal nerve.These studies were performed on adult Japanese White rabbits, anesthetized with urethane and alfa-chioralose. The trachea was cannulated and a catheter placed in femoral artery. Arterial pressure and heart rate were calculated from pressure wave of femoral artery. Mental nerve was stimulated with 10S train of squarewave pulses (0.5mS duration). Records of nerve activities were obtained from cervical sympathetic nerve and vagal nerve.In preliminary study, we determined that the optimal frequency and intensity range which evoked trigeminal depressor response was 5Hz and 5-20mA.In this study, mental nerve was stimulated in these manners.We examined two volatile anesthetics (isoflurane and sevoflurane ) and one intravenous anesthetic (propofol).In isoflurane and sevoflurane, degree of fall in blood pressure became smaller as inspired concentration of anesthetics became higher. TDR disappeared in almost 0.75-1.0 MAC ( tail clamp method). 1.0 MAC of tail calmp method is said to be equivalent to plane 3 or 4 of third stage in Guedel's clinical signs. It is suggested that concentration necessary to suppress TDR is rather high in isoflurane and sevoflurane.On the other hand, effects of propofol on TDR were minimum. In administration rate of 125 mg/kg/hr, which was extremely high dosage, about 8% of fall in blood pressure evoked with mental nerve stimulation was observed. So we concluded that propofol could not disappear TDR completely. It is suggested that proper blocked of noxious stimulation is necessary when general anesthesia is performed with propofol for oral surgery.